The positive
charges collect near the upper edges of
the clouds and the negative charges
accumulate near the lower edges. There
is an accumulation of positive charges near
the ground also. When the magnitude
of the accumulated charges becomes very
large, the air which is normally a poor
conductor of electricity is no longer able
to resist their flow. Negative and positive
charges meet, producing streaks of
bright light and sound. We see streaks
as lightning. The process is
called an electric discharge.